Geometry Puzzle

A neat little puzzle from John Mason.

How are the blue and red area related?

Equal of course! To see this, we label the regions.

2+4+7 forms half of the rectangle;
3+4+5 also forms half of the rectangle.
So in total twice the blue region and once the white regions sum up to the area of the whole rectangle.
On the other hand the blue, red and white regions also sum up to the area of the whole rectangle.
Ergo, area of blue equals area of red.

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